The present invention relates to a hydraulic brake system having a master cylinder, and brakes which are connected to the master cylinder so as to receive the output oil pressures from the master cylinder and provide braking forces to the wheels of a vehicle.
In prior-art hydraulic brake system of the type specified above, as disclosed in the official gazette of Japanese Utility Model Registration Application Laid-Open No. 77068/1987 by way of example, the oil pressures delivered from the master cylinder in accordance with the magnitude of tread of a brake pedal are controlled by hydraulic control units and then supplied to the brakes. Meanwhile, when a car is to start on the surface of a road exhibiting a low coefficient of friction, for example, a snowcovered road or a frozen road, it is sometimes the case that the driving wheels of the car slip for a very short time, to grind the road surface and to lower the coefficient of friction further. If, on such an occasion, brake pressures can be controlled at quick response, the starting performance of the car can be enhanced. With the prior-art system, however, such a control of the brake pressures is impossible.